High-pressure rubber hose is used in many instances in industry but particularly in the mining, construction, energy, marine and petrochemical industries. Flexible rubber hose is used to transfer fluids under various pressures and temperature between two points, one or both of which, may move relative to each other or to another fixed point in space. Piping at the two points is generally metal (or some other form of fixed conduit) and the flexible hose must attach to the piping at both ends. This requires a coupling on each end of the hose.
In the drilling industry, a flexible rubber hose runs between the pump piping system on the rig and the kelly that is coupled to the rotating drill string. The pump system forces drilling fluid down the center of the drill pipe, and back through the wellbore, in order to flush cuttings from the wellbore (plus providing wellbore stability, etc.). In this instance, the flexible hose is subjected to high pressures. The high pressure is required to both transfer drilling fluid into the wellbore and overcome static return head pressures—the deeper the wellbore, the higher the pressure.
The rotary drilling hose is subject to further stress in that it hangs down within the derrick supported at either end by the metal coupling on the hose and the fact that the kelly is moved up and down literally thousands of times during the drilling operation. This means that the hose is subject to stress at the metal coupling (in addition to being subject to stress throughout its length). Thus, a highly reliable bonding between the hose and the coupling is required for protection of personnel and equipment. If the hose breaks loose from the coupling, it could easily fall and cause severe damage on the drill floor of the rig. In a similar manner, if the hose breaks, circulation may be lost resulting in a well blowout situation.
In order to obtain a high-pressure flexible rubber hose (the term rubber is used generally and does not specifically mean natural occurring rubber gum), a hose manufacturer incorporates a reinforcing material. Thus, the hose will consist of an inside sealing membrane—the fluid tight element, an inner rubber element, a reinforcing element, an outer rubber element, and finally some sort of abrasive resistant covering. The reinforcing element can be polyester or similar organic material, carbon fiber or similar high technology material or metal (steel) generally in the form of wire or cable. The reinforcement generally is used in multiple layers called “plys” And usually made of steel.
There are four types of reinforcing employed by the hose manufacturer that is set down in even layers—i.e., 2 layers, 4 layers, 6 layers, etc., and a grading systems are used to specify burst pressures for hose. For example, in the rotary drilling industry, grade C hose has a minimum burst pressure of 10,000 psi, grade D hose has a minimum burst pressure of 12,500 psi and grade E hose has a minimum (guaranteed) burst pressure of 18,750 psi. Grade C and D hose are 2 ply hose, although there is some 4 ply D hose. Most grade E hose is 4 ply. Swage end connectors are currently available for two ply hose and therefore the burst pressure range for C and D hoses is covered by the current art.
Generally a hose manufacturer manufactures flexible hoses to specific order by the purchaser who specifies length, diameter, pressure, service ratings and required end connections. These flexible hoses are generally referred to as a “hose assembly with end connectors.” This term is used throughout the industry.
It takes time to manufacture a hose assembly with end connections and often such a hose is needed almost immediately by industry. In order to service this demand a separate industry termed the local market distributor has evolved. The local market distributor keeps bulk reinforced hose—hose without connectors—in inventory. The purchaser would specify the hose requirements—diameter, length, pressure rating and end connectors—to the local market distributor. The local market distributor then takes bulk reinforced rubber hose from inventory, cuts the hose to required length, and places a coupling on each end of the hose. Bulk hose is available in varying lengths from a hose manufacturer, and the actual bulk length (between 90 and 110 feet) will depend on the mandrel used by the manufacturer.
The resulting hose is called a SWAGED or CRIMPED HOSE, depending on the method used to “place” the end connector onto the hose, where the term “place” is being used to include both swaging and/or crimping operations. It should be noted that swaging and crimping accomplish similar end results.
The current state of the art in swaged (or crimped) connectors has evolved to using an outer ferrule with lands (internal ridges) that are compressed around the end of a reinforced hose about a stem that is inserted into the end of the hose. The stem may or may not have barbs that are meant to improve the “grip” between the hose and the end connector. Often, the outer layer of hose rubber is “skived” which means that the outer layer of rubber is removed exposing the reinforcement (although some local distributors do not skive).
The reinforced hose is actually held in the end connector by the ridges of the ferrule gripping the reinforcement via compression of the hose against the stem. The compression operation (swaging or crimping) of the ferrule against the reinforcement and against the inner stem creates severe stress and strain within the rubber of the hose and in particular the reinforcement.
It is known that multiple ply-reinforced hose may contain manufacturing defects (actually all reinforced hose may contain defects). During manufacture a ply may be out of position. That is, rather than lie next to each other a void (filled of course with rubber) may exist between the plys; the plys may be off-center; or, one or more cables may stand out (i.e., be slightly above the other cables). These defects can cause failure, if the defect is within or near the confines of the swaged or crimped connection.
The reason for the failure is relatively simple and relates back to stress imposed on the plys by the end connector. If a cable or ply is out of place, that element will be compressed more than the other elements. This additional compression puts more stress on the out-of-place reinforcement that can result in failure.
Development of high pressure swaged end connectors for rubber hose has extended over a period of years and the art runs the gauntlet from low temperature and/or low pressure to high temperature and/or high pressure applications. The hose diameters range from fractional inches (fractional centimeters) to tens of inches (fractional meters) and the manufacturers/providers of connectors realize that the pump-off force on the fitting is proportional to the inside diameter of the hose and the applied pressure.
For example, Marco (U.S. Pat. No. 3,073,629) discloses a low temperature end connector designed to clamp about the helical reinforcing employed with a particular type of hose used in cryogenics. Marco employs the standard ferrule and stem used throughout the industry while shaping the two parts to interact with the helical reinforcing. Moss (U.S. Pat. No. 3,165,388) discloses a device directly intended to resolve pump-off experienced with flexible hoses under various temperatures and pressure. Moss uses the standard two-part connector and discloses a ferrule that is designed to bite into the outer fabric of the hose therefore using stress to retain the hose within the connector. Moss further discloses a mandrel that is inserted in the stem during the swaging operation to keep the internal hose from being damaged.
Most of the art uses a serrated stem that has backward facing teeth that grips the inner liner of the hose to retain the stem in the hose. Much of the art also uses a series of lands (ridges) within the ferrule that bite into the outer layer of the hose and the reinforcement and supposedly causes the teeth (or barbs) of the stem to bite further into the inner lining. (See Moss above.) Some art realizes that stress in the hose should be avoided and Flounders (U.S. Pat. No. 3,540,486) proposes a smooth ferrule that extends the stress over a larger area; however, Flounders relies on a serrated stem to hold the connector on the hose.
Szentmihaly (U.S. Pat. No. 4,106,526) looks at stress in the hose itself and proposes a connector that is designed to allow expansion chambers within the ferrule to accept the excess elastomeric (rubber) flow caused when the connector is crimped about the hose and utilize that flow to hold the connector in place. Szentmihaly teaches that narrow extrusion gaps with parabolic shaped expansion chambers will substantially prevent extrusion of the elastomer liner in hose in the axial direction. The narrow extrusion gap (less than 60-thousandths of an inch) and the associated expansion chambers prevent elastomer flow during the crimping operation thereby making the elastomer behave as if it is incompressible. Szentmihaly further teaches that the radial movement of the ferrule will cause the ferrule to move the hose reinforcement to follow the shape of the expansion chambers thereby forcing the elastomer into the chambers. At no point does Szentmihaly discuss axial movement and distortion that would occur in large diameter fittings which require extrusion gaps very much larger than 60-thousandths.
Fourier et al. disclose a specially shaped ferrule and stem designed to first screw onto the hose and then be swaged onto the hose. Again the device holds the connector in place by gripping the elastomer of the hose. Similar art may be found in Smith (U.S. Pat. Nos. 4,544,187 and 4,684,157), Chapman et al. (U.S. Pat. No. 5,317,799), Beagle et al. (U.S. Pat. No. 5,199,751) and Haubert et al. (U.S. Pat. No. 4,548,430—an interesting three part device).
In order to grip the hose more securely the art currently uses lands or ridges within the outer ferrule to grip the reinforcement found within high pressure hose. The hose can be skived (the outer layer of the hose removed to expose the reinforcement under the fitting) or not skived. Currie et al. (U.S. Pat. No. 4,366,841) modifies the well known art by supplying a series of backward facing lands on ferrule that face the same direction as the serrations on the stem that will penetrate the hose, grip the reinforcement, distort to the shape of the hose and thereby hold the hose in place. Patel et al. (U.S. Pat. No. 4,407,532) is concerned with the force required to swage (crimp) the ferrule and proposes a device that grips the hose reinforcement with a ferrule that has reduced material thereby reducing the crimping force.
Wilson (U.S. Pat. Nos. 5,382,059; 5,487,570 and 5,607,191) proposes a grooved stem with ridges that is designed to better accept the crimping force that is transferred through the hose to the inner stem. The grooved stem allows for expansion of the elastomer into the grooves thereby reducing the force transferred to the stem and utilizes a hoop structure to further reinforce the stem. The device uses standard ridges in the ferrule that may grip the hose reinforcement. Kozuka et al. (U.S. Pat. No. 5,344,196) disclose a serrated stem with an annular groove that receives the expanded rubber (elastomer) thereby providing a better grip on the inner rubber liner. The outer ferrule is internally smooth before crimping; however, when it is crimped the resulting series of grooves are used to act as lands thereby further gripping the rubber. Other variations use a ridged ferrule. The shape of the ferrule serves no particular function but to act as a method of gripping the rubber.
Burrington (U.S. Pat. No. 4,564,223) proposes a device which has ridges in both the ferrule and the stem. The ferrule differs little from the prior art; however, Burrington discloses at least one ridge on the stem that is opposite to a corresponding ridge on the ferrule. Thus when the Burrington device is crimped or swaged the opposite ridges produce a pincher-like grip on the reinforcement which bites into the reinforcement. It should be apparent that device can cause great stress in the reinforcement.
Thus, there remains a need for swaged or crimped hose end connectors that will extend the range of diameter and pressure applications for swaged (or crimped) hose, that will work with rotary drilling hoses and other industry hose, that will work with multiple ply spiral cable or wire plys, that will work with most types of reinforcement, that will compete with integral end connections, that will reduce or eliminate stress points in the reinforcement and that will accept a reasonable range of defective, but safe, hose.